1. Field of the Invention
The common rail injection system provides high-pressure injection of fuel into direct-injection internal combustion engines. In this reservoir injection system, pressure generation and injection are decoupled from one another both chronologically and in terms of location. A separate high-pressure pump generates the injection pressure in a central high-pressure fuel reservoir. The injection onset and the injection quantity are determined by the instant and duration of the triggering of electrically actuated injectors, which communicate with the high-pressure fuel reservoir via fuel lines.
2. Prior Art
German Patent Disclosure DE 100 01 099 A1 relates to a control valve for an injector of a fuel injection system. The control valve includes a final control element and is actuated by an actuator. By means of the control valve, a hydraulic communication between a fuel return and a control chamber of the injector can be established. When the control valve is opened, fuel flows from the control chamber into the fuel return. As a result, the pressure in the control chamber drops, and the hydraulic force acting on the end face of the nozzle needle decreases. As soon as this hydraulic force is less than the hydraulic force acting in the opening direction, the nozzle needle opens, so that the fuel can flow through the injection ports of the injection nozzle into the combustion chamber. This indirect triggering of the nozzle needle via a hydraulic force booster system is necessary because the great forces required for fast opening of the nozzle needle cannot be generated directly by the control valve.
German Patent Disclosure DE 196 50 865 A1 relates to a magnet valve for controlling an electrically controlled fuel injection valve. The valve needle of the fuel injection valve is urged in the closing direction by pressure prevailing in a control chamber. The magnet valve, to initiate the injection, initiates a relief of the control chamber when the magnet of the magnet valve is excited. The valve needle of the injection valve is then lifted from its seat, under the influence of the high pressure acting upon it in the opening direction.
In the prior art, in addition to the fuel quantity injected into the combustion chamber, a so-called “control quantity” is required for indirectly triggering the valve needle. Upon opening of the magnet valve, a control quantity reaches the low-pressure region of the fuel tank via the magnet valve and a control quantity line. Upon closure of the magnet valve, the control valve switches to a different switching position, in which once again a control quantity occurs. For maintaining a master pressure required for the function of the control valve, a pressure holding valve with an inlet throttle upstream of it is used in a further control quantity line, through which the control quantity flows away from the control valve. Downstream of the pressure holding valve, the control quantities from the magnet valve and from the control valve flow in a common line as a total leakage quantity into the low-pressure region. Accordingly, the pressure holding valve serves not only to maintain the aforementioned master pressure but also to separate the pressure potentials of both control quantities (that of the control valve and that of the magnet valve).
In this prior art injector, however, pressure fluctuations in the control quantity line from the control valve occur upon switching of the control valve; they are propagated as far as the valve needle of the magnet valve, and in the least favorable case they can cause unwanted opening of the magnet valve.